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Recap – Formula and bonding
Types of bonding: ionic, covalent, metallic
Types of formula: empirical, molecular, structural
Type of covalent materials: molecular, network
1
H N
H
H
H2O2HO H O O H
2
Polarity of Water
• The O-H bonds in water are polar.• The angular shape of the molecule
mean water is a ‘polar molecule’.
Fig.
4.2
Sil
berb
erg
3
Chemical Reactions
Chemical reactions occur because:
• Products contain less energy than reactants and systems go to lowest energy state, eg burning gas.
• Energy supplied to force reactants to products which have higher energy, eg blast furnace.
4
Chemical Equations
• Word Equationhydrogen plus oxygen forms water
• Symbolic Equations – use correct formula
H2 + O2 H2O
• Need to balance equations. Indicate states
2H2(g) + O2(g) 2H2O(l)
5
Chemical Equations
• Molecular Equationeg H2(g) + I2(g) 2HI(g)
C6H12O6(s) C6H12O6(aq)
• Ionic Equations eg NaCl (s) Na+(aq) + Cl-(aq)
Pb2+(aq) + 2I-(aq) PbI2(s)
Precipitate
6
Reactions with Acid, H+
- e-
H+Hydrogenatom
Hydrogenion
• H+ cation is just a ‘bare proton’, no e-.
• In aqueous solution, H+ associates with H2O to give H3O+(aq), also called H+(aq).
+OH H
H
• Substances that provide H+ ions in water are called ACIDS.
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Metal + Acid Salt + Hydrogen
Formula EquationZn + 2HCl ZnCl2 + H2
Complete ionic equation Zn(s) + 2H+(aq) + 2Cl-(aq) Zn2+(aq) + H2(g) + 2Cl-
(aq)
Net ionic equationZn(s) + 2H+(aq) Zn2+(aq) + H2(g)
We can isolate the salt by evaporation of the solvent
Zn2+(aq) + 2Cl-(aq) ZnCl2(s)
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Carbonate + Acid Salt + H2O + CO2
Formula EquationCaCO3 + 2HCl CaCl2 + H2O
+ CO2
Complete ionic equation CaCO3(s) +2H+(aq) + 2Cl-(aq) Ca2+(aq) + H2O(l) +
CO2(g) + 2Cl-(aq)
Net ionic equationCaCO3(s) + 2H+(aq) Ca2+(aq) + H2O(l) +
CO2(g)
We can isolate the salt by evaporation of the solvent
Ca2+(aq) + 2Cl-(aq) CaCl2(s)
• By the end of this lecture, you should:− understand the reason that water dissolves some
ionic materials− know the component parts of a chemical equation− be able to balance a chemical equation− recognise a molecular equation, formula equation
and an ionic equation− be able to describe a chemical reaction in terms of
a chemical equation− understand an acid supplies H+ ions and exists in
water− recognise reactions involving dissolution,
precipitation and acids
− be able to complete the worksheet (if you haven’t already done so…)
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Learning Outcomes:
10
Questions to complete for next lecture:
1. Balance the following chemical equations:
a) CH4(g) + O2(g) CO2(g) + H2O(l)
b) CaCl2 + AgNO3 Ca(NO3)2 + AgCl
c) Ag+(aq) + CrO42-(aq) Ag2CrO4(s)
d) Ca(s) + H+(aq) Ca2+(aq) + H2(g)
e) Mg(OH)2(s) + H+(aq) Mg2+(aq) + H2O(l)
2. Classify the above equations as ‘molecular’, ‘formula’, or ‘net ionic’.
3. Which of the equations in question 1 represent a precipitation reaction?
4. Which of the equations in question 1 represent a reaction with acid?
5. Would it matter if you used hydrochloric acid or sulfuric acid to perform the reaction represented by equation 1d?
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